Section 909 of the penal code of state S provides that it is
unlawful to possess in a motor vehicle any alcoholic beverage except those
contained in bottles sealed with unbroken state tax stamps. On June 1,
State Police Officer Obie stopped D for speeding. While writing
out the ticket Obie saw on the seat a half-full bottle of Old Redneck
100 proof sourmash bourbon with fragments of a torn state tax stamp around
the neck of the bottle. Obie confiscated the bottle, and shortly thereafter
D was charged with violation of Section 909 of the Penal Code.

At D's trial Obie is the star witness. On direct examination
Obie testifies to the facts set forth above. The D.A. then produces a
half-full bottle of Old Redneck, has the clerk tag the bottle as People's
Exhibit A for identification, and asks Obie if he recognizes it. Obie
says that he recognizes the bottle as the bottle confiscated from D
on June 1. The D.A. then offers the bottle into evidence. Defense counsel
asks the court for permission to take the witness on voir dire for the
purpose of making an objection to the admission of the bottle. The court
grants defense counsel's request. On voir dire counsel shows Obie three
other identical half-full bottles of Old Redneck (which secretly contain
iced tea) and asks Obie how he distinguishes between the offered exhibit
and the three other bottles presented to him.

What mistake in police administration has Obie made? What principle of
evidence relating to the handling of real evidence has Obie violated?